When using a video colposcope for cervical or other examination, the user at times needs to view the subject area via the equivalent of a green filter to enhance vascular discrimination. In prior art embodiments, this is accomplished either by placing a conventional green filter between the subject area and the optics of the colposcope, or by illuminating the subject area with a green light source. The conventional green filter removes much of the red portion of the light. The conventional filters add cost, mechanical complexity, and reduce the total light energy available, which can degrade the quality of the final image. Positioning a separate light to illuminate the entire area with a green light source is inconvenient, adds cost, and can interfere with use of the colposcope.
While considering alternative ways to provide effective green-filter imaging of the cervix without the disadvantages of illumination-path or optical-path light filtering, the idea arose of using electronic modification of color in the video images produced by the colposcope to electronically reproduce the effect of an optical green filter.
Electronic modification of color in video images is well known, but has not been applied previously to colposcopy. The present invention effects a novel method and apparatus for using electronic modification of color to remove appropriate colors for the image so as to emulate the effect of placing an optical filter in the illumination or optics path of a video colposcope.
It is desired to provide a video colposcope that can be used to electronically produce images on a monitor that appear similar to those from conventional optical colposcopes that use an optical green filter.
It is also desirable to provide switch activation for the green filter effect in a colposcope to replace the mechanical knob or slide activation system used in conventional optical systems.
It would also be desirable to provide a green filter in a colposcope that eliminates the need for cleaning an optical filter or for a special green lighting apparatus.
Further, it would be desirable to provide an optimal green filter effect for a colposcope that is insensitive to the color of the available lighting.
Additionally, it would be desirable to provide a variable or otherwise selectable green filter effect in a colposcope.
Accordingly, the apparatus of the present invention comprises a video colposcope with an electronic color filter that can be switched on and off by a user, including storage means for storing reference data defining reference filter color balance levels, a video camera for obtaining an electronic image of a subject object, color balancing circuitry for modifying color saturation, hue, and intensity levels of the subject electronic image according to the reference filter color balance levels to produce a modified electronic image corresponding to the subject electronic image, and output means for outputting the modified electronic image to a display means in real time as the corresponding subject electronic image is obtained by the video camera.
In the method of the present invention, data defining reference filter circuitry or algorithms for color balance levels are stored in a storage means. A video camera obtains a subject electronic image of a subject object, and, using either color balancing analog circuitry or algorithm driven digital signal processing circuitry, color saturation, hue, and intensity levels of the subject electronic image are modified. This modification occurs according to the analog reference filter color balance levels or to the digital signal processing algorithm as stored in the storage means, thus producing a modified electronic image corresponding to the subject electronic image. The modified electronic image is outputted to a display means in real time as the corresponding subject electronic image is obtained by the video camera.
One embodiment of the invention for a video colposcope used as a diagnostic instrument comprises a video camera module combined with a light source and application-specific lenses. The video camera block is implemented with analog or digital signal processing technology. In digital signal processing technology the video image is represented as a pattern of digital bits (data) rather than as a collection of analog signals employed by a traditional video camera. Since the image exists as a numerical representation (data), processing can be done on the data that represents the signal (i.e., an image), rather than on the analog signal itself. With digital signal processing, functions such as equalization and filtering are realized by performing mathematical operations on the image data, rather than by using discrete electronic circuits.
By implementing the filter function as an algorithm to be performed on the data representing the image, rather than as a physical implementation, the green filter effect is achieved by processing the data set that comprises the image with an algorithm that produces the desired image information. Since the algorithm runs on the digital signal processing circuitry contained within the camera, there is no incremental cost except for the switch to turn the filter function off and on. The digital signal processing implementation has the additional potential for variable filter characteristics, with only an algortihm (or filter coefficient) change. The digital signal processing filter algorithm can also include a provision to "white balance" the resulting green-filtered image--essentially modifying the ratio of the remaining colors to approximate their prominance (or weight) if the camera were focused on a white scene. This provides a more pleasing representation to the human eye, while maintaining the advantages of the green-filtered image.
A user control means can be used to turn the filter function on and off. The user control means can be a simple switch or button, or any other method of allowing the user to turn the filter function on and off.
The invention can be made potentially less costly than conventional systems by use of inexpensive IC electronics and switches. Other advantages include switch activation (as opposed to a mechanical knob or slide used in conventional optical systems), selectable emulation of green filter characteristics (as opposed to using available optical green filter characteristics only), and the potential for variable filter characteristics, selectable by the user during use.
The invention involves replacing the conventional green filter of an optical colposcope with electronic reduction of the amplitude of at least one color in the video signal. For vascular discrimination using a colposcope, an optical green filter is emulated by decreasing the red portion of a video signal (not all the red is removed because a typical optical green filter passes some red light). Because the reduction is accomplished electronically (e.g., by analog means or by digital signal processing), the amount of this red reduction can be varied so as to optimize the characteristics of the electronic filter for vascular discrimination. Any changes needed in the characteristics of the filter can be easily made in the factory, or even by the user of the colposcope.
Emulation of some green filters can also require that the blue content of the signal be reduced. Again, since this reduction is made electronically, it can be implemented along with the red signal reduction to allow easy change in the factory or by the user.